What's with the one on the bottom left? Everyone else has a fair amount of detail and shading but that one looks straight ms paint. It looks like the creator just said fuck it while working on the last one.

When an artist makes an image electronically, like through photoshop, they often have several different layers that they build upon. Some of those layers are drafting of what they're going to paint next, in the same way that a traditional painter will sketch out their subject with pencil on the canvas before applying paint. My guess is this piece just isn't completely finished, and that little area is work in progress.